RADIO CONSTRAINTS on LONG-LIVED MAGNETAR REMNANTS in SHORT GAMMA-RAY BURSTS

Wen-fai Fong, B. D. Metzger, E. Berger, F. Özel

Research output: Contribution to journalArticlepeer-review

27 Scopus citations

Abstract

The merger of a neutron star (NS) binary may result in the formation of a rapidly spinning magnetar. The magnetar can potentially survive for seconds or longer as a supramassive NS before collapsing to a black hole if, indeed, it collapses at all. During this process, a fraction of the magnetar's rotational energy of ∼1053 erg is transferred via magnetic spin-down to the surrounding ejecta. The resulting interaction between the ejecta and the surrounding circumburst medium powers a year-long or greater synchrotron radio transient. We present a search for radio emission with the Very Large Array following nine short-duration gamma-ray bursts (GRBs) at rest-frame times of ≈1.3-7.6 yr after the bursts, focusing on those events that exhibit early-time excess X-ray emission that may signify the presence of magnetars. We place upper limits of ≲18-32 μJy on the 6.0 GHz radio emission, corresponding to spectral luminosities of ≲(0.05-8.3) × 1039 erg s-1. Comparing these limits to the predicted radio emission from a long-lived remnant and incorporating measurements of the circumburst densities from broadband modeling of short GRB afterglows, we rule out a stable magnetar with an energy of 1053 erg for half of the events in our sample. A supramassive remnant that injects a lower rotational energy of 1052 erg is ruled out for a single event, GRB 050724A. This study represents the deepest and most extensive search for long-term radio emission following short GRBs to date, and thus the most stringent limits placed on the physical properties of magnetars associated with short GRBs from radio observations.

Original languageEnglish (US)
Article number141
JournalAstrophysical Journal
Volume831
Issue number2
DOIs
StatePublished - Nov 10 2016

Keywords

  • gamma-ray burst: general
  • stars: magnetars
  • stars: neutron

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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